The following systems are available for transmitting current data between multi-terminal current differential relays used in a conventional current differential relay system. A first type of system provides one-to-one transmission whereby each current differential relay is provided with channels whereby it can exchange current data individually with all other current differential relays. Next is a multicast transmission system, in which a channel such as for example a LAN (local area network) is provided and each current differential relay transmits current data to all other current differential relays through the LAN (Local Area Network). Next, a bucket relay type transmission system may be provided, in which all of the current differential relays are connected by a single loop-form channel, the current differential relays receive current data transmitted in a predetermined direction through this channel, and the current data that is received is transmitted to the next current differential relay, being appended to the current data of the terminal that received the aforementioned current data. Also available is the representative terminal identification transmission system, in which current data is concentrated onto a representative current differential relay. The representative terminal identification transmission system is adopted in cases where it is impossible to employ any of the one-to-one transmission system, multicast transmission system or bucket relay type transmission system. In the representative terminal identification transmission system, if a fault is detected, the representative current differential relay transmits a breaker trip signal for clearing the fault to each current differential relay, using the channel that is employed for current data collection. Such a system is disclosed in Laid-open Japanese Patent Application Number 2009-284758 (hereinafter referred to as Patent Reference 1).
However, the aforementioned transmission systems have the following respective problems. Specifically, in the case of the one-to-one transmission system, a considerable amount of communication processing and communication volume are involved, so there is a limit to the number of current differential relays that may be provided in such a current differential relay system. In the case of a multicast transmission system, when the number of current differential relays provided in the current differential relay system becomes large, the reception processing at each current differential relay is increased. In the case of a bucket relay type transmission system, when the number of current differential relays provided in the current differential relay system becomes large, the cumulative transmission time lag becomes large. In the case of a representative terminal identification transmission system, when the number of current differential relays provided in the current differential relay system becomes large, reception processing at the representative current differential relay is increased.
According to an aspect of the present technology, an object of the present invention is to provide a current differential relay system wherein, even when a large number of current differential relays are provided in a current differential relay system, by exchanging current data between current differential relays, the reception processing of each current differential relay is reduced and the network load can be reduced, and a current differential relay employed in such a system.
In order to achieve the above object, the present embodiment is constructed as follows. Specifically, a current differential relay that is employed in a current differential relay system that is used to protect a transmission line connecting installations by a plurality of current differential relays comprises: an interface section; a quantization section; a communication section; and a difference calculating section. The interface section receives current supplied from the aforementioned transmission line. The quantization section quantizes this received current and converts it to first current data. In the case where the communication section is a representative current differential relay of a first group formed of some current differential relays of the aforementioned plurality of current differential relays, the communication section receives second current data from another current differential relay belonging to the aforementioned first group, transmits the aforementioned second current data and the aforementioned first current data jointly to a representative current differential relay belonging to the second group, receives third current data from the aforementioned representative current differential relay, and transmits the aforementioned third current data to the aforementioned other current differential relay. The difference calculation section executes current difference calculation using the aforementioned first to third current data.